On 03/28/2013 03:53 PM, Tudor Popescu wrote: > I was wondering if anybody is able to help with (any one of) these > questions? That would be really helpful, as I could not find an answer > on the wiki. > > Many thanks in advance! > > On 26 March 2013 20:44, Tudor Popescu <tud...@gmail.com > <mailto:tud...@gmail.com>> wrote: > > Hi everyone, > > > My QDEC analysis ran into an error message that seems to be a > "classic" (and, so far, it seems unsolved), from mri_concat, which > I've described in a separate message, just sent. > > > I have, however, more theoretical questions about QDEC, which I > hope some kind soul will help me with: > > > - why does QDEC only provide the volume of /subcortical/ > structures under StatsDataImport/aseg.volume, when the automatic > GM/WM segmentation is done for the entire brain, not just for > subcortical regions? > No reason in particular. You can add them into the qdec table. > > > - how are the volume measurements provided in aseg.volume > different from the ones done obtained with a VBM analysis? > Does VBM give segmentation volumes? I thought it was voxel-wise exploratory. > > - why is /volume /the result of /segmentation /(aseg.volume) > whereas /thickness /derives from /parcelation > /(rh.aparc.thickness)? Is it not the case that both operations > (segmentation+parcellation) are necessary to calculate volume as > well as thickness? > You can get volume from parcellations too (this is supplied in the ?h.apac.stats file). You can't get thickness from non-surface structures like amygdala. > > > - how is a QDEC thickness analysis different from a regular > AN(C)OVA in which you are interested in main and interaction > effects of the IVs on the DV? I ask this because some of the > questions that appear in QDEC's Analysis Results tab – e.g. "is > the correlation between (DV) and (IV) different from zero?" – > would not (I think) be directly answerable by an ANOVA > Often times they are the same, depends on the contrast. I don't know what IV and DV are so I can't answer your specific question. > > - would the same type of ANOVA done by QDEC be doable by > extracting the values of the DV for each subject (using e.g. > /aseg.volume/) and then doing the ANOVA in e.g. SPSS? If so, when > would you do one versus the other? > Yes. QDEC is an exploratory voxel-based method so effects don't have to lie cleanly within an ROI boundary. > > - why is it that only continuous factors (e.g. age) can be taken > in the analysis as nuisance factors, when discrete variables (e.g. > gender) might also be irrelevant for a particular analysis and > thus belong to the Nuisance Factor list? > It is just a matter of convenience in making the contrasts. ie, it is easy to extend our contrast making code to add nuisance continuous variables doug > > Many thanks in advance!! > > Tudor > > > > > _______________________________________________ > Freesurfer mailing list > Freesurfer@nmr.mgh.harvard.edu > https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
-- Douglas N. Greve, Ph.D. MGH-NMR Center gr...@nmr.mgh.harvard.edu Phone Number: 617-724-2358 Fax: 617-726-7422 Bugs: surfer.nmr.mgh.harvard.edu/fswiki/BugReporting FileDrop: www.nmr.mgh.harvard.edu/facility/filedrop/index.html Outgoing: ftp://surfer.nmr.mgh.harvard.edu/transfer/outgoing/flat/greve/ _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer The information in this e-mail is intended only for the person to whom it is addressed. If you believe this e-mail was sent to you in error and the e-mail contains patient information, please contact the Partners Compliance HelpLine at http://www.partners.org/complianceline . If the e-mail was sent to you in error but does not contain patient information, please contact the sender and properly dispose of the e-mail.
